KR100354727B1 - Solid electrolyte membrane with mechanically-enhancing and porous catalytically enhancing constituents - Google Patents

Abstract

The solid electrolyte ion-permeable membrane may comprise a substrate material that conducts at least one type of ion such as oxygen ions and one or more constituents that can be physically distinguished from the substrate material and that can improve the sintering action, ≪ / RTI > The components are present in such a way as to prevent continuous electronic conduction through the constituents of the film. The porous film containing the gas element is preferably arranged on the film to improve the surface reaction rate.

Description

TECHNICAL FIELD [0001] The present invention relates to a solid electrolyte membrane having improved mechanical and catalytic properties,

The present invention relates to a solid electrolyte ion-permeable membrane having at least one component that improves the composition of the solid electrolyte ion-permeable membrane, in particular, the mechanical properties, the catalytic properties, and the sintering action of the membrane.

The present invention has been accomplished by the Government of the United States under cooperative agreement No. 70NANB5H1065, which was implemented by the National Institute of Standards and Technology. The US Government has certain rights to the invention.

The solid electrolyte ion-permeable membrane has a great possibility of separating oxygen from the oxygen-containing gas stream. In particular, there is a growing interest in mixed conducting materials that can conduct both oxygen ions and electrons and operate in a pressure driven mode without the use of external electrodes. A composite ceramic mixed conductor membrane composed of a polyphase mixture of an electron conductive material and an oxygen ion conductive material is used in an electrochemical reactor and a partial oxidation reaction. second. Is described in U.S. Patent No. 5,306,411 to Majanek. M. U.S. Patent No. 5,478,444 to Liu et al. Describes a composite mixed conductor material containing an oxygen-ion-conductive material such as bismuth oxide and an electron-conductive material. _{La .2 Sr .8 CoO X, La} .2 Sr .8 FeO X, La .2 Sr .8 Fe .8 Co .1 Cr .1 O True mixed conductors, exemplified by a perovskite (perovskite), such as _X Are materials with high conductivity for both electrons and ions. Some of these materials have a known maximum oxygen ion conductivity and a rapid surface exchange kinetics.

While these materials have high potential when applied to gas separation, they have some drawbacks when used for such applications. A common problem with most ceramic materials is their brittleness and low mechanical strength at tension, making it difficult to fabricate large elements such as tubes and making it difficult to place these materials in commercial systems that require high reliability.

Yamomoto et al., LaCoO sintered in a paper entitled " Perovskite type oxide as an oxygen electrode for a high temperature oxide fuel cell ", Solid State Ion Science (1997), 22: 241-46_x Of the microcracks. Such microcracks are associated with structural deformation during sintering and frequently occur in perovskite. The vacancy concentration in most ion permeable membrane materials, such as perovskite, is a function of the partial pressure of oxygen in the gas surrounding it. Since the unit cell size depends on the vacancy lattice point concentration, in most ion permeable membrane materials, P₀₂The volume of the unit cell is increased. For example, in the perovskite, the unit cell ABO₃Increases as the partial pressure of oxygen on the anode or permeate side decreases. The change in the unit cell size causes not only the composition expansion coefficient but also the thermal expansion coefficient. Thus, the composition gradient in the material creates a mechanical stress that can cause failure. This often necessitates precise control of the atmosphere during start-up and shutdown of the work or during the process.

ratio. (Y _1-X Ca _X ) FeO ₃ , a potential cathode material for solid oxide fuel cells, at the Third International Symposium on Solid State Oxide Fuel Cells, and Ss. Singh Edward, 93-4, 276-282 (1993) reported that microcracking is a problem in Y _1-X (Sr or Ca) _X MnO ₃ due to either the highly anisotropic thermal expansion coefficient of the system or the thermophilic polymorphic symmetry change. However, their efforts to address these problems have not been successful, because they can reduce microcracks with high Sr and Ca doping levels (x> 0.3), but due to poor physical properties, including reduced ionic conductivity, Resulting in poor performance.

Due to the difficulties described above, the fabrication of perovskite tubes sometimes requires complex and meticulous process control steps involving sophisticated atmospheric controlled sintering processes. This increases cost and manufacturing complexity and can cause problems during instantaneous operation of manufactured elements, including temperature, atmosphere or composition changes.

It is highly desirable to minimize the sensitivity of the ion-permeable membrane to ambient air. In addition, most of these materials have a very high coefficient of thermal expansion (e.g., La _1-x Sr _x CoO ₃ is about 20 x 10 ^-6 / ° C), which causes high thermal stresses during processing and during operation Thereby causing destruction of the material.

In summary, the use of composite mixed conductors in the prior art is largely limited to the materials that comprise a polyphase mixture of oxygen ion conductors and electron conductors. The main purpose in the prior art was to introduce electronic conductivity into the ion conductor. Generally, this requires that the electronically conductive second phase be present in excess of 30 to 35% by volume when randomly distributed to be operable above the percolation threshold.

Shen et al. Describe in column 6 of U.S. Pat. Nos. 5,616,223 and 5,624,542 that the silver / palladium alloy in one system can achieve a continuous phase at about 20 to about 35% by volume, although a slightly higher amount is required have. Shen et al. Prefer to present an electronically conductive phase in an amount of about 1 to 5% in order to obtain a high bipolar conductivity. The '542 patent describes a ceramic / metal material having a predominantly electronically conductive metal phase that provides improved mechanical properties over the predominantly ionically conductive ceramic phase alone.

Composite bulk superconducting materials were synthesized to obtain desirable physical properties and high T _C superconducting properties. In U.S. Patent No. 5,470,821, Wong et al. Describe composite bulk superconducting materials having continuous superconducting ceramics and elemental metal matrices. The elemental metal is located in the space between the crystalline particles to increase the transmission current density.

The permeation of oxygen is driven by the partial pressure of oxygen in the air stream. Nernst potentential is generated internally as described in the copending U.S. Patent No. 5,547,494, referred to herein as " stepped electrolyte membrane ", and the oxygen vacancy lattice point Of the flux.

In general, a thin electrolyte film is preferred because an ideal oxygen flux is inversely proportional to the thickness of the film. Thus, thinner films result in higher oxygen flux, reduced area, lower operating temperature and lower oxygen pressure differential across the electrolyte. Also, when the anode side of the membrane is purged by reactive gases such as methane or hydrogen, the oxygen activity on the anode side is significantly reduced, leading to a high oxygen flux across the membrane. However, as the oxygen flux increases, the surface resistance to permeation becomes more intense and ultimately dominates the overall resistance to permeation. Surface resistance arises from a number of mechanisms involved in converting oxygen molecules in the gas phase into oxygen ions in the crystal lattice and acting in opposition. Even in the case of dense ion-permeable membranes, surface kinetics on the cathode or anode side can limit the oxygen flux across the membrane.

The solid state gas separation membranes reported by Yasuta Haderaoka et al., Ceramic Journal Society International, Vol. 97, No. 4, pp. 458-462 and 5 523-529 (1989) On a mixed support. A relatively thick porous mixed conducting support provides mechanical stability to a dense, thin, relatively brittle, conductive layer. Taking into account the thickness of the dense layer, the inventors have predicted that the oxygen flux will increase ten times in the case of thin composite film membranes as compared to dense mixed conducting disks. However, they obtained an increase in oxygen flux of less than 2 times using a thin film film.

U. S. Patent No. 4,791, 079 describes a catalytic ceramic membrane consisting of two layers, namely impermeable mixed ion and electron conductive ceramic layers and a porous catalyst-containing ion conductive ceramic layer. A preferred composition for the porous ceramic layer is zirconia stabilized with about 8 to 15 mole percent of calcia, yttria, scandia, magnesia, and / or mixtures thereof.

U.S. Pat. No. 5,240,480 describes a composite solid state membrane, which comprises a dense layer and a multi-component metal oxide porous layer capable of separating oxygen from the oxygen-containing gas mixture at high temperatures.

U.S. Patent No. 5,569,633 describes a surface catalyzed multilayer ceramic membrane comprising a dense mixed conducting multi-component metal oxide layer and a catalytic metal or metal oxide coating on the feed (air) side to enhance oxygen flux. The catalyst coating on both sides failed to improve the oxygen flux.

It is therefore an object of the present invention to provide an improved solid electrolyte ion permeable membrane having improved mechanical properties.

It is still another object of the present invention to provide a solid electrolyte ion permeable membrane that minimizes microcracks during fabrication.

It is another object of the present invention to provide a solid electrolyte ion-permeable membrane that does not require a special atmosphere during processing or operation.

Still another object of the present invention is to provide a solid electrolyte ion permeable membrane adapted to changes in temperature and atmosphere.

It is yet another object of the present invention to provide a solid electrolyte ion permeable membrane that significantly reduces the limit imposed by surface kinetics and / or chemical kinetics to obtain a high oxygen flux.

It is another object of the present invention to provide a solid electrolyte ion permeable membrane having a modified surface that provides an improved catalytic effect to the ion permeable membrane.

1A to 1D are enlarged photographs of membranes having different amounts of components according to the present invention.

Fig. 2 is a graph showing the breaking strength for the four films shown in Figs. 1A to 1D.

FIG. 3 is a graph showing the results of X-ray diffraction for the films of FIGS. 1A-1D. FIG.

FIG. 4 is a graph showing the oxygen permeability at various temperatures in the films of FIGS. 1A to 1D. FIG.

FIG. 5 is a chart showing oxygen fluxes at various reaction purge levels for the membranes of FIGS. 1A-1D. FIG.

6A is a scanning electron micrograph of another film according to the present invention.

FIG. 6B is a surface energy dispersion spectrum of the film shown in FIG. 6A. FIG.

7 is an enlarged cross-sectional view of a dense solid electrolyte ion permeable membrane having a porous crystalline layer coating for enhancing surface reaction according to the present invention.

8 is an enlarged cross-sectional view of a solid electrolyte ion-permeable membrane composite having a porous crystalline layer coating on both surfaces of a dense membrane to enhance surface reaction, one of the porous coatings being applied on a porous support to improve the mechanical strength of the composite .

Description of the Related Art [0002]

701, 801: ion conductive films 702, 703, 802, and 803:

804, 805:

The present invention relates to a process for the production of a matrix material having at least one ionic type, preferably a matrix material, which conducts oxygen ions, and at least one constituent which is physically distinct from the matrix material and which improves its mechanical, catalytic, and / And a solid electrolyte ion permeable membrane. The components are present in such a way as to prevent continuous electron conduction across the membrane through this component.

In a preferred embodiment, the matrix material is a mixed conductor that exhibits both electronic conductivity and oxygen ion conductivity. The component is preferably a metal such as silver, palladium, or mixtures thereof. In another embodiment, the component is a ceramic or other electrically non-conductive material.

The invention also includes a solid electrolyte ion-permeable membrane composite for separating gas species from a gas mixture, said composite having a dense matrix material and a porous coating. Wherein the dense film has a first and a second surface and is comprised of a matrix material that conducts one or more ion types and at least one film component physically distinct from the matrix material, In a manner that improves at least one of the mechanical properties, catalytic properties, and sintering behavior of the membrane and prevents continuous electron conduction through the membrane across the membrane. The porous coating is disposed on at least one of the first surface and the second surface of the membrane to enhance the surface kinetics associated with the gas species.

As used herein, the term " dual phase " refers to a combination of a phase that conducts one or more ionic types and a phase that includes such components.

The term " ion-permeable material ", as used herein, is also interchangeable with " matrix material ".

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of preferred embodiments and accompanying drawings.

The present invention can be achieved with a solid electrolyte membrane, wherein the membrane is physically distinguishable from at least one ionic type, preferably a matrix material that conducts oxygen ions, and is physically distinct from the matrix material and has mechanical, catalytic, At least one of which can improve at least one of the components. The component is present in such a way as to prevent continuous conduction of electrons across the membrane through the component.

Thus, the present invention relates to a multiphase composite material, which prevents the formation of a first mixed conductor phase, such as perovskite, and microcracks during manufacture, eliminating special atmospheric control during processing and operation, A second component capable of improving mechanical properties, cyclability, atmospheric cyclability and / or surface exchange rate compared to when only a conductor image is present.

The present invention provides compositions with improved mechanical and, preferably, catalytic properties without degrading the oxygen permeability, by introducing a suitable second component phase into the mixed conductor. Such a second phase can alleviate the compositional stress and other stresses generated during sintering, prevent the propagation of microcracks in the mixed conductor phase, and significantly improve the mechanical properties (especially tensile strength). Since the atmospheric control can be removed during the sintering process, it is easy to increase the manufacturing scale and the cost is reduced. The ability to remove atmospheric control during thermal cycling facilitates the use of a membrane in a more robust real system for changes in temperature or gas composition.

The present invention can also be achieved by a solid electrolyte ion-permeable membrane composite having a dense membrane and porous coating for separating gas components from the gas mixture. The dense film comprising a matrix material having first and second surfaces and conducting at least one ionic type and comprising at least one of mechanical, catalytic and sintering properties of the matrix material, , This component is present in such a way as to prevent continuous electron conduction across the membrane through this component. The porous coating is deposited on one of the first and second surfaces of the membrane to enhance the surface reaction rate associated with the gas species.

The present invention provides a composition having improved catalytic properties by introducing a porous coating onto a multi-phase dense solid electrolyte ion permeable membrane to improve surface kinetic exchange for the dense membrane. The porous coating significantly improves catalytic activity or surface exchange kinetics when only the dense electrolyte permeable membrane is present.

The porous coating layer is deposited on the reactive surface of the dense membrane. For purposes of illustration, when purging the anode side of a composite membrane according to the present invention with a methane containing gas, the surface reaction rate of methane can be significantly increased by providing a large surface area on the membrane surface.

This is especially true when the porous layer is deposited on the anode side of the membrane because the rate limiting step is generally on the anode side of the membrane when the reactive component of the purge gas is methane. There may be a particular chemical reaction where there is a rate limiting step on the cathode side of the membrane. In such a case, the porous coating is deposited at least on the cathode side.

In one preferred embodiment, the coating is deposited on the surface of both the anode side and the cathode side. This is particularly preferred because it allows easy manufacture of a double-coated dense film.

Depositing a coating layer on either side of the dense matrix material balances the coating to prevent or reduce the possible effect of mechanical stress on the film surface. Upon curing, the porous coating can generate mechanical stress on one side of the dense matrix material if the coating is formed on only one side. It is therefore desirable to deposit the coating layer on both sides of the dense matrix material to reduce the unbalanced stresses that result from the coating.

The dense membrane of mixed conducting oxide that permeates oxygen ions has infinite oxygen / nitrogen selectivity. Examples of such materials are given in Table 1 and examples thereof include various oxides having a structure that can be derived from oxides such as perovskite structure or brown millerite, A ₂ B ₂ O ₅ . A common problem with such ceramic membranes is the brittleness and low mechanical strength during tension making it difficult to fabricate large elements such as tubes and to use them in high-reliability commercial systems. These limitations prevent mixed conductors such as peroxides and microcracks during fabrication in air compared to using only mixed conductor phases, improve mechanical properties, improve thermal / atmospheric cyclability and increase surface exchange rate Which is composed of a suitable second component, such as a metal, for improving the properties of the second component.

Suitable ion-permeable membrane materials include ionic conductors and mixed conductors that can permeate oxygen ions. When used in accordance with the present invention, the ion-permeable material comprising the first phase preferably transmits both oxygen ions and electrons irrespective of the presence on the second component. A more comprehensive description of the first phase material to which the second component phase may be added in accordance with the present invention is given in the following examples.

In another embodiment, suitable ion permeable membrane materials include mixed conductors capable of permeating oxygen ions. When used in accordance with the present invention, the mixed conductor phase can transmit both oxygen ions and electrons irrespective of the presence of the second electron conduction phase. Examples of mixed conducting solid electrolytes of the present invention are provided in Table 1 below, but the present invention is not limited to the composition of the materials summarized in the above table. A dense matrix material other than a material consisting solely of mixed conductors is also contemplated by the present invention.

Table 1: Mixed Conducting Solid State Electrolytes

Composition of materials One. (La _1-x Sr _x ) (Co _1-y Fe _y ) O _{3 -?} (0 _{? X ?} 1, 0 _{? Y ?} 1, 2. _{SrMnO 3-δ SrMn 1-X} Co X O 3-δ (0≤x≤1, 0≤y≤1, δ from _{stoichiometry) Sr 1-X Na X MnO} 3-δ 3. _{BaFe 0.5 Co 0.5 YO 3 SrCeO 3} YBa 2 Cu 3 O 7-β (0≤β≤1, δ from stoichiometry) 4. La _0.2 Ba _0.8 Co _0.8 Fe _0.2 O _2.6 ; Pr _0.2 Ba _0.8 Co _0.8 Fe _0.2 O _2.6 5. _{A x A 'x' A "} x" B y B 'y' B "y" O 3-Z , where (x, x ', x " y, y', y" are all 0 to 1 range Im), A , A ', A "are selected from 1,2,3 and f-block lanthanides and B, B', B" are selected from d-block transition metals 6. (a) Co-La-Bi type: 15 to 75 mol% of cobalt oxide 13 to 45 mol% of lanthanum oxide 17 to 50 mol% of bismuth oxide (b) Co-Sr-Ce type: 15 to 40 mol% of cobalt oxide (C) Co-Sr-Bi type: cobalt oxide 10 to 40 mol% strontium oxide 5 to 50 mol% bismuth oxide 35 to 70 mol% (c) Co-La- Ce type: cobalt oxide 10 to 40 mol% lanthanum oxide 10 to 40 mol% cerium oxide 30 to 70 mol% Co-La-Sr-Bi type: cobalt oxide 15 to 70 mol% lanthanum oxide 1 to 40 mol% Strontium oxide 1 to 40 mol% bismuth oxide 25 to 50 mol% Co-La-Sr-Ce type cobalt oxide 10 to 40 mol% lanthanum oxide 1 to 35 mol% strontium oxide 1 to 35 mol% cerium oxide 30 To 70 mol% 7. _{Bi 2-xy M 'x M} y O 3-δ (0≤x≤1, 0≤y≤1, δ from stoichiometry) where, M' _x is Er, Y, Tm, Yb, Tb, Lu, Wherein M is Mn, Fe, Co, Ni, Cu, and mixtures thereof, wherein M is at least one element selected from the group consisting of Nd, Sm, Dy, Sr, Hf, Th, Ta, Nb, Pb, Sn, In, 8. BaCe _1-x Gd _x O _{3-x / 2} where x ranges from 0 to 1

9. A _s A _'t B _u B' _v B _"W O _X family, and their compositions are described in (such as as soon as the neck), U.S. Patent 5,306,411 and as follows: A is a lanthanide or Y, or a mixture thereof; A 'is an alkaline earth metal or a mixture thereof, B is Fe, B' is Cr or Ti, or a mixture thereof, B 'is Mn, Co, V, Ni or Cu, t is from about 0.01 to about 100; u is from about 0.01 to about 1; v is from 0 to about 1; W is from 0 to about 1; (X + v + w) < 1.1 where x is a number satisfying the valence of A, A ', B, B' 10. One of La _1-x Sr _x Cu _1-y M _y O _3-d family material, where M is Fe or Co; x is 0 to about 1, and; y is 0 to about 1, and; d is in the composition formula La, Sr, Cu and M 11. Ce _1-x A _x O _{2 -d} family material, wherein A is lanthanide, Ru or Y; Or mixtures thereof, x is from 0 to about 1, and d is a number satisfying the valency of Ce and A in the composition formula 12. One of the Sr _1-x Bi _x FeO _{3 -d} family materials, where x is from 0 to about 1, y is from 0 to about 1, and d is a number satisfying the valence of Ce and A in the composition formula 13. Where x is from 0 to about 1, y is from 0 to about 1, z is from 0 to about 1, and w is the valence of Sr, Fe, and Co in the composition formula: Sr _x Fe _y Co ₂ Ow family material It is a satisfying number. 14. Dual phase mixed conductors (electronic / _{ionic): (Pd) 0.5 / (} YSZ) 0.5 (Pt) 0.5 / (YSZ) 0.5 (B-MgLaCrO x) 0.5 (YSZ) 0.5 (In 90% Pt 10%) 0.6 / (YSZ _{) 0.5 (in 90% Pt 10} %) 0.5 / (YSZ) 0.5 (in 95% Pt 2.5% Zr 2.5) 0.5 / (YSZ) _0.5 high temperature the metal (e.g., Pd, Pt, Ag, Au , Ti , Ta, W) is added to the above-mentioned material.

In general, the matters to be considered in selecting the material on the second component are as follows. (1) Coordination of the thermal expansion coefficient (TEC) between the second phase and the ion permeable material. (2) Chemical compatibility between the second phase and the ion permeable material. (3) Good bond between the second phase and the matrix of ion permeable material. (4) Flexibility of the second phase to relieve stresses during sintering and cooling. (5) low cost. The TEC coordination is important because normal stresses are created in and around the second phase when the composite material is cooled from fabrication. Selection of an incorrect second phase material may lead to peeling or cracking due to thermal stress induced during fabrication and operation. This can be minimized by reducing the difference in the two thermal expansion coefficients between the ion-permeable material and the second phase. In another embodiment, the ion-permeable material is described as a matrix material and the second phase is described as a constituent.

Chemical compatibility is important because it causes degradation of the material by high temperature operation and treatment of the ion permeable material, and interactions and mutual diffusion between the ion permeable material and the second phase, which may degrade the performance of the membrane, are caused. Therefore, the second phase should not react undesirably with the ion permeable material or be chemically inert thereto to prevent adverse interactions and interdiffusion at high temperatures.

A good bonding force is important because peeling occurring between the second phase and the ion-permeable material may adversely affect the strength of the material. Cracks and crevices can easily diffuse, causing breakage of the material.

The flexibility of the second phase component is important because many ion permeable materials have very high thermal expansion coefficients. High TECs cause high thermal stresses during processing and operation of the ion permeable material, which can lead to material failure. The flexibility of the second phase can release stresses generated during sintering and / or cooling.

In addition to the above considerations, the catalytic activity of the second phase preferably improves the surface kinetics of the composite ion-permeable membrane. Therefore, increased catalytic activity can reduce the high cost of a given component or electronic conduction phase.

The constituent component phase according to the invention is not electronically continuous across the iontophoretic membrane. However, the constituent components may be physically continuous when formed of a non-electroconductive material. It is preferred that the randomly distributed electronically conductive component is less than 30% by volume to ensure that the component is present in such a way that it is below the percolation limit of the electrons passing through the film.

The second component phase may be selected from two or more alloys of metals such as silver, palladium, platinum, gold, rhodium, titanium, nickel, ruthenium, tungsten, tantalum or the like that are stable at the operating temperature of the film. Suitable high temperature alloys include Inconel, Hastelloy, Monel, and Duke Rolls. Silver, palladium, or silver / palladium alloy is preferable. The second phase is also selected from ceramics such as an oxidized praseodymium-indium mixture, a niobium oxide-titanium mixture, titanium oxide, nickel oxide, tungsten oxide, tantalum oxide, ceria, zirconia, magnesia, or mixtures thereof . Some ceramic second phases, such as titanium oxide or nickel oxide, may be introduced in oxide form and then reduced to metal during operation in a reducing atmosphere.

Another method for carrying out the present invention is to use a physically continuous non-electroconductive second component such as glass, asbestos, ceria, zirconia or magnesia fibers or wire, or a piece of material such as a mica to reinforce the ion- Lt; / RTI > The continuous second phase is distributed substantially uniformly in the ion permeable matrix, structurally reinforcing the ion permeable membrane and improving the mechanical properties of the ion permeable membrane. The diameter of the fibers is usually less than 1 mm, preferably less than 0.1 mm, more preferably less than 0.01 mm, and most preferably less than 1 탆. Typically, the aspect ratio (length to diameter) is greater than 10, preferably greater than 100, and more preferably greater than 1000.

Hereinafter, the composite ion-permeable membrane containing mixed conductive La _{. 2} Sr _.8 Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x and silver / palladium alloy second phase will be described in detail.

≪ Example 1- La _.2 Sr _.8 Fe _.69 Co _.One Cr _.2 Mg _.01 O _x And 50Ag / 50Pd alloy with improved mechanical properties>

A mechanically enhanced ion permeable material was prepared from 50 wt.% Ag and 50 wt.% Pd Ag / Pd alloy (hereinafter referred to as 50Ag / 50Pd alloy) available from Degussa Corporation, Sausalpurane Field, ₂ Sr _.8 Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x (available from SSC, Inc. of Udineville, Pa. (Now PSC Observation Air Surface Technology, Inc.) Mixed conductor powders were prepared by mixing for 15 to 20 minutes at various weight ratios (5, 10, and 20 wt%) using a SPECS mixer (SPECS Industries, Inc., Edison, NJ). The powder was then added to a 2-propanol solution containing 3 wt% PVB (Butvar of Monsanto, St. Louis, Mo.), mixed by a magnetic stirrer at 80 캜 for evaporating 2-propanol, And sieved through a mesh size of 74 mu m before pressing. Mechanically enhanced membrane disks were prepared using a 1.5 "die at 10.4 kpsi pressure and then burned (25 ° C to 400 ° C at 1 ° C / min and held for 1 hour) And sintered at 1250 DEG C for 2 hours at a cooling rate.

The microstructures of the sintered discs were examined using an optical microscope and a scanning electron microscope (SEM) together with energy dispersion spectroscopy (EDS) to analyze the chemical composition. X-ray diffraction (XRD) analysis was performed using a Rigaku Miniflex diffractometer with Cu K? radiation to study the compatibility of the second phase with the ion permeable membrane. Mechanical strength was measured at room temperature by a three point bend test using a 19 mm span and a crosshead speed of 0.5 mm / min using an Instron tensile tester. The sample (30 × 4 × 3 mm) was produced by pressurizing with cooling at 30 kpsi after dry uniaxial pressing, and sintering at 1250 ° C. for 2 hours. All specimens were cut and polished using a synthetic diamond disk prior to testing to prevent any edge defects. The test was performed with five specimens for each composition. The oxygen permeability was measured using a sintered disk specimen sealed in an aluminum test cell with a gold paste. The permeation test was carried out at 900 to 1000 DEG C with a He inert gas purge and a different reactive purge gas. HP 5890 gas chromatography, oxygen analyzer and humidity analyzer were used to analyze the gas composition and calculate the oxygen flux.

The goal of the mechanically improved ion permeable material is to increase the mechanical strength of the iontransmitting matrix and possibly to eliminate the need for a nitrogen atmosphere during sintering. The initial result of this test was to improve the mechanical strength of the iontransmitting material disk by reducing the composition stress and other stresses generated during sintering of the second phase (Ag / Pd alloy) and preventing the propagation of micro-cracks in the mixed conductor phase . Figure 1 shows that the sintered ion-permeable material disk's crack density can be significantly reduced by increasing the amount of the second phase. The effect of the second phase concentration on the fracture strength of the ion permeable material by the 3 dumb bend test is indicated by curve 90 in Fig. The results show that the breaking strength of the ion permeable material increases significantly (from 0 to 175 MPa) as the second phase increases from 0 to 20 wt%. The use of Ag / Pd alloys significantly reduced the crack density and increased the mechanical strength of the iontophoretic disk. It is believed that this is due to the metal phase, which improves the mechanical strength of the dual phase iontophoretic disk by preventing the growth of cracks while reducing the composition stress during sintering. The XRD results shown in Figure 3 show that after sintering at 1250 占 폚, a 20% Ag / Pd alloy (spectrum 100) and La _{.2 Sr.8} Fe _.69 Co _.1 Cr _.2 Mg _.01 &_lt; / RTI &_gt; O _x (spectrum 102).

Oxygen permeation tests were performed on 0.85 mm discs at 900-1000 < 0 > C temperature under an air / helium atmosphere at a flow rate of 500 sccm (standard cubic centimeters per minute) for each stream at 1.2 atm pressure. The oxygen flux was 0.5, 0.7, and 0.9 sccm / cm 2 at 900, 950 and 997 ° C, respectively (curve 110), and was 1.0 (as compared to the active energy obtained for the single phase specimen eV. < / RTI > Therefore, the use of the second phase did not appear to reduce the oxygen permeability of the material.

Testing of the dual phase disc was performed at 1000 캜 using different concentrations of H ₂ (10 and 20%) / N ₂ mixture on the purge side. As the H ₂ concentration on the reaction side increased from 10% to 20%, the O ₂ flux increased from 4.6 to 9.4 sccm / cm 2. Compared to the single-tube test, dual phase disks also exhibited higher oxygen flux under the same reactive purge conditions as shown in FIG. This is believed to be due to an improvement in the surface oxidation kinetics due to the catalyst properties of the second phase.

≪ Example 2 - Synthesis of La _.2 Sr _.8 Fe _.69 Co _.One Cr _.2 Mg _.01 O _x And 65Ag / 35Pd alloy with improved mechanical properties>

Dense dual phase discs of 20% 65Ag / 35Pd (65 wt% Ag and 35% wt% Pd) and La _.2 Sr _.8 Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x , The procedure of Example 1 was repeated except that 50Pd was changed to 65Ag / 35Pd. At room temperature N ₂ permeation test, the disc was confirmed to be gas-tight. The scanning electron micrograph at 5180 magnification in FIG. 6a shows a second phase well distributed in the La _{. 2} Sr _.8 Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x matrix, But did not exhibit peeling, indicating good compatibility between the ion-permeable membrane and the second phase. The surface EDS (Energy Dispersive Spectroscopy) spectrum of the specimen (Figure 6b) also shows the minimum composition loss of the second phase and matrix after sintering. The ratio of Pd to Ag in the second phase after sintering (0.548) was close to the ratio of 65Ag / 35Pd alloy (0.538) within the accuracy of the gauge. The disk showed good mechanical strength after sintering at 1200 < 0 > C in air and no fine cracks were found. The oxygen permeation test was carried out with a 0.9 mm disk at 1000 < 0 > C temperature under air / helium gradient. The O ₂ flux was 0.8 sccm / cm 2 at 1000 ° C comparable to the oxygen flux of the dual phase specimen of Example 1 (containing 20wt% of 50Pd / 50Ag second phase). The reactive purging test on the disk was performed at 1000 ° C using a 10% H ₂ -90% N ₂ mixture on the purge side. An O ₂ flux of 4.5 sccm / cm ₂ was obtained at 1000 캜, which is comparable to the flux value of the dual phase specimen having a 20 wt% 50Pd / 50Ag alloy.

Example 3 - Ion-permeable membrane improved in mechanical properties of La _{. 2} Sr. ₈ Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x and 90 Ag / 10 Pd alloy.

The _{La .2 Sr .8 Fe .69 Co .1} Cr .2 Mg .01 O x and the 90Ag / 10Pd of 20wt% dense dual phase disc of the second phase as 50Ag / 50Pd (fraction's Air Technologies, Inc. Was replaced with 90Ag / 10Pd. ≪ tb >< TABLE > The disc and bar were prepared by burning the binder under dry pressure of 10.4 kpsi (25 ° C to 400 ° C at 1 ° C / min for 1 hour) and burning in air at a heating / cooling rate of 2 ° C / min for 1 hour And sintered at 1200 ° C. Although these specimens showed no microcracks, the specimens showed low mechanical strength (average 135 Mps) compared with the 20 wt% 50Ag / 50Pd alloy containing dual phase specimens. This can be attributed to the low tensile strength of the 90Ag / 10Pd alloy compared to the 50Ag / 50Pd alloy. The oxygen permeation test was carried out with an extruded tube (10 cm in length after sintering, 1 mm in inner diameter, and 1 mm in wall thickness) at a temperature of about 1000 캜 under a reactive purge test using various purge gases. The flux of oxygen was slightly lower (about 10-15%) than the dual phase tube with 50Ag / 50Pd alloy under similar test conditions. Oxygen flux of 2.2 sccm / ㎠ at 1025 ℃ was obtained as a purge gas containing 60% CH ₄ for the tube.

With respect to a more generally suitable first phase material, the microcracks can have an ABO ₃ perovskite structure as a result of phase transformation during sintering and cooling, or a structure that can be derived from the structure (e.g., , A ₂ B ₂ O ₅ ). The microcracks were reduced in La _{. 2} Sr _.8 Fe _.69 Co _.1 Cr _.2 Mg _.01 O _x perovskite by adding various amounts of Ag / Pd second phase as shown in Examples 1 and 2 . The invention described herein is A _r A _'s A _"t B _u B' _v B" _w O _x there is structural formula intended to cover suitable mixed conducting oxides are represented, in the structural formulas A, A, 'A "is B and B'B "are selected from D-block transition metals and 0 <r ≤ 1, 0 ≤ s ≤ 1, selected from lanthanide elements of Group 1, 2, 3 and F blocks according to the elemental periodic table adopted by IUPAC , 0? T? 1, 0? U? 1, 0? V? 1, 0? W? 1, and x is a number that makes the compound charge neutral. Preferably, in the structural formula A, A 'or A "is a Group 2 metal selected from the group consisting of magnesium, calcium, strontium and barium. Preferred mixed conducting oxides are expressed by a composition formula A _s A' _t B _u B _'v B" _w O _x wherein A represents lanthanide, Y or a mixture thereof, A 'represents an alkaline earth metal or a mixture thereof, B represents Fe and B' represents Cr, Ti, or a mixture thereof S, t, u, v and w each represent a number of 0 to about 1, and B " represents Mn, Co, V, Ni, Cu or a mixture thereof.

Suitable first phase materials also include other ion conductive ceramics that can occur during sintering due to high temperature polymorphic symmetry changes, composition stress, or a high anisotropic coefficient of thermal expansion. For example, zirconia exhibits phase transformation at 1170 ° C (monoclinic to tetragonal) and 2370 ° C (tetragonal to cubic). High temperature polymorphic symmetry changes usually cause cracking during sintering. Therefore, zirconia is stabilized to a cubic system cubic phase by introducing an appropriate bivalent or trivalent oxide to obtain cubic symmetry. The present invention is also intended to include improvements in the mechanical properties of other ceramics such as zirconia or ceria in the context of high temperature polymorphism symmetry changes, composition stresses or very anisotropic thermal expansion coefficients. In addition, it has been found that in order to form a film having at least three phases, an electron / ion conductor such as (B-MgLaCrO) _0.5 (YSZ) _0.5 , or a conductor in the predominant ion such as zirconia or ceria combined with perovskite, May be further combined with the components.

Other embodiments of the present invention are directed to coating a dense membrane by depositing a porous coating on at least one surface of the membrane. It is believed that the coating modifies the surface of the membrane to provide a catalytic effect during ion transmission as well as provide structural stability to the surface layer.

The drawings of the present invention show specific embodiments of the solid electrolyte ion-permeable membrane composite of the present invention. 7 shows the porous coating layers 702 and 703 deposited on both side surfaces of the dense solid electrolyte ion conductive membrane 701. Fig. 8 shows another embodiment in which the porous coating layers 802 and 803 are deposited on both side surfaces of the dense solid electrolyte ion conductive film 801. Fig. The membrane 801 is supported on a porous support comprising an intermediate support layer 804 and a support layer 805 and a porous coating layer 803 is present between the membrane 801 and the intermediate support layer 804.

While there may be a number of methods for depositing a material layer on a dense surface, one preferred manufacturing method is to immerse the dense membrane into a liquid precursor (e.g., slurry, colloidal solution) of the porous coating, Drying and curing the coating. This method is a much easier and more economical method for depositing the porous coating layer on a dense surface compared to other methods available in the art.

Suitable ion permeable membrane materials include mixed conductors that can permeate oxygen ions. When used in accordance with the present invention, the mixed conductor phase can transmit both oxygen ions and electrons irrespective of the presence of the second phase electron conduction phase. Examples of mixed-conducting solid electrolytes of the present invention are provided in Table 1 above, but the present invention is not limited to the compositions of the materials listed in the above table. A dense matrix material other than a material consisting solely of mixed conductors is also contemplated by the present invention.

Suitable coating compositions can be composed of mixed conducting oxides having electron conductivity as well as permeating oxide ions. Examples of porous coated mixed conductors are given in Table 1 above and may be the same or different from the mixed conducting oxide of the dense film. As with the dense film, the coating may comprise a composition having a mixed conductor phase and a coating component.

Suitable porous coating compositions comprise a combination of a coating composition and a mixed conductor capable of transmitting oxygen ions and / or electrons. Mixed conductors can conduct oxygen ions and conduct electrons independently of the coating components. It is preferred that the coating components constitute less than about 30% by volume of the total porous coating.

Porous coatings can be coated using a number of methods known to those skilled in the art. A preferred method is a slurry dip coating process. Such a method is preferable due to its ease of use and cost efficiency in coating a dense film. Other methods include physical vapor deposition (PVD) such as spin coating, chemical vapor deposition (CVD), electrochemical deposition (EVD), laser ablation and sputtering, thermal spraying, plasma spraying, RF plasma deposition, .

The porous coating layer should be thinner than the surface of the dense membrane to improve the surface reaction rate of the dense membrane. Thus, the porous coating layer has a thickness of less than about 50 탆, preferably less than 10 탆, more preferably less than 5 탆.

A more detailed description of the porous coating according to the present invention is given in the following examples.

In yet another embodiment, a porous support can be used to enhance the structural stability of the membrane. The porous support may comprise inert ion conductive, mixed conducting and electron conductive (metal) materials, or mixtures thereof. In addition, the porous support may contain catalytic property enhancing components with either inert ion conductive, mixed conducting, and electron conductive materials, or mixtures thereof. Porous supports are particularly important where the dense matrix material is thin and fragile. Structurally, it is preferred that at least one of the dense membrane and the porous coating is deposited on the porous support. An example of such an embodiment is shown in Fig. 8 as described above.

Example 4

One days on the dense _{La .2 Sr .8 Fe .69 Co .1} Cr .2 Mg .01 O x ( "LSFCCM") powder (SSC) solid electrolyte ion conducting tube (inner diameter 7.1㎜, 9.7㎜ outer diameter, length about 15 Cm) was extruded and sintered at 1250 占 폚 in a nitrogen atmosphere for 1 hour at a heating / cooling rate of 2 占 폚 / min. In order to test the oxygen permeability across the tube, the following procedure was followed. (Containing 30% of an inert gas such as N ₂ or Ar bubbling through the water, 60% of CH ₄ and 10% of CO ₂ ) was caused to flow inside the tube in the direction of countercurrent flow of the feed gas . The temperature of the purge gas flowing through the tube, referred to as the " ion permeation temperature &quot;, was monitored with a thermocouple located halfway below the ion permeable membrane tube. Oxygen in the feed gas was partially removed by permeation across the ion permeable membrane to yield a product that was lean in oxygen. The volumetric fraction (X _F ), the product O ₂ volume fraction (X _P ) and the volumetric flow rate ('P' sccm) of the feed O ₂ were measured and the feed volume flow (F) The following mass balance for the permeable species, P (1-x _p ) = F. (1-x _F ), was calculated. The O ₂ flux across the ion permeable tube was calculated by the following equation.

O ₂ - flux = (Fx _{F -} Px _p ) / A _{ion permeability}

Here, A _{ion permeation} = area (cm 2) of the average ion permeable tube through which O ₂ permeates.

Example 5

Example 5 shows a specific example of the electrolyte membrane according to the present invention. A single-phase dense LSFCCM solid electrolyte ion conducting tube similar to the tube of Example 4 was prepared. The tubes were coated using a slurry dip coating process with a Chemat Technology Model 201 to place a porous layer having particles of about 1 micron size of single-sided LSFCCM ion permeable material on both surfaces of the tube.

Thereafter, the coated material was tested in the same manner as in Example 4. The improvement of the O ₂ flux across the ion permeable membrane due to the aid of the porous coating is shown in the following table based on experimental data. In experiments conducted under similar conditions, the coated ion permeable tubes exhibited a significantly higher O ₂ flux (4 times) than the uncoated ion permeable tubes. In this case, data related to a similar feed flow rate appeared. The coated monolith tube was observed to separate more oxygen from the simulated feed stream.

It is noted that the supply O ₂ volume fraction used in the coated tube test is slightly higher than the uncoated tube test. However, according to Wagner's theory, the O ₂ flux depends on the logarithm of the supply O ₂ volume fraction. Therefore, even if the O ₂ volume percentage in the feed stream changes from 20.9 to 22.6, it is not expected to have a significant effect on the average flux recorded in the following table.

Table 2: Results for single-ion permeable membrane tubes

Tube area (㎠) O _{2 in the} feed O _{2 in the} product Feed flow rate (sccm) Product flow rate (sccm) Ion permeation temperature (캜) Average flux (sccm / cm2) Uncoated single-sided ion permeable tube (Example 4): 38.5 20.9% 17.41% 329 315 1,001 0.4 Single-phase ion-permeable tube (Example 5) having a 20 mm porous coating of 1 mm single- 37.6 22.6% 0.50% 322 205 1,021 1.6

Example 6

A dual-phase iontransmission tube of LSFCCM containing 20 wt% 50Ag / 50Pd (50 wt.% Ag and 50 wt.% Pd) was prepared by slip casting. Dual phase LSFCCM ion permeable membrane slip 20wt% 50Ag / 50Pd alloy (DeGussa) and _{La .2 Sr .8 Fe .69 Co .1} Cr .2 Mg .01 O x powder (SSC) and 2 drops of commonplace (Darvan) C The dispersion was prepared by mixing with water at a solid phase concentration of 35%. This slip was pulverized for 5 hours, slip cast in a gypsum mold, and sintered at 1250 ° C for 1 hour at a heating / cooling rate of 2 ° C / min. The double-phase tube was tested in the same manner as described in Example 4.

Example 7

Example 7 shows another embodiment of the present invention. A double-phase LSFCCM iontransmission tube similar to the tube of Example 6 was prepared. The tubes were coated using a slurry dip coating process with a sieve matte technology model 201, which was used to place a porous layer of about 1 micron size of single-phase LSFCCM ion permeable material on both surfaces of one of the tubes, The tube of Example 6 was left uncoated. A substantial improvement in O ₂ -flux (3.8 times) was observed with respect to the porous single-phase ion-permeable layer disposed on the tube. In this example, a data point related to a similar product O ₂ concentration was selected. A much higher feed stream was used in the coated dual phase tube to separate O ₂ in similar amounts.

Example 8

Example 8 shows another embodiment of the present invention. An extruded double-phase LSFCCM iontransmission tube similar to that of Example 4 was prepared. The tubes were slit immersion coated with a body matte technology model 201, which was used to place a porous layer of about 1 micron size on a dual-phase LSFCCM ion permeable material containing LSFCCM and constituents on both surfaces of one of the tubes Lt; / RTI &gt; The component consisted of 50Ag / 50Pd and was about 20 wt.% (About 11 vol.%) Of the total porous layer. A significant improvement in O ₂ -flux (3.7 times) was observed with respect to the porous single-phase ion-permeable layer disposed on the tube. In this example, a data point related to a similar product O ₂ concentration was selected. A much higher feed stream was used in the coated dual phase tube to separate O ₂ in similar amounts. It also appears that significant improvements in O ₂ product, feed stream and product stream can be obtained.

Table 3: Results for double-phase ion permeable tubes

Tube area (㎠) O _{2 in the} feed O _{2 in the} product The calculated feed flow rate (sccm) Product flow rate (sccm) Ion permeation temperature (캜) Average flux (sccm / cm2) a. Uncoated single-phase iontransmission tube (Example 6): 17.5 20.9% 5.57% 209 175 1,034 1.9 b. Single-phase ion-permeable tubes with a 20 mm porous coating of 1 mm single-phase ion-permeable granules (Example 7) 17.8 20.9% 5.34% 790 660 1,062 7.3 c. Single-phase iontransmission tubes with a 20 mm porous coating of 1 mm double-phase iontransmitted granules (Example 8) 37.7 20.9% 12.92% 2,884 2,620 1,017 7.0

In each example, it is noted that in an ion permeable tube having a mixed conductor and an electron conductor porous layer, the oxygen flux is increased approximately four times that of a dense uncoated ion permeable tube.

Example 9

Dual phase discs were fabricated. Both surfaces of the sintered disc were polished to a thickness of 0.9 mm. The oxygen permeation rate was measured on the disk at 900 DEG C under air / helium atmosphere. The disk specimen was sealed in an alumina test cell with Ag paste. The composition of the gas was analyzed using an HP 5890 gas chromatograph and an oxygen analyzer, and the oxygen flux was calculated. The flux test results (sccm / cm 2) at 900 ° C are summarized in Table 4.

Example 10

Example 10 shows another embodiment of the electrolyte membrane according to the present invention. A double-phase disc similar to that of Example 9 was prepared and polished to a thickness of 0.6 mm.

A number LSFCCM ion permeable material drop similar to that of Example 5 was deposited on the surface of a disk fixed on a spin coater. The strained layer was deposited using a spin speed of 3500 rpm for 20 seconds. After spin coating, the deposited coating of the LSFCCM ion-permeable material on the disk was dried on a hot plate at 80 DEG C for 5 minutes and then transferred to a hot plate with a ceramic top and heated at about 300 DEG C for at least 5 minutes. The entire coating and drying process was repeated until a 1 m LSFCCM film was formed on the surface of the membrane. Thereafter, the dual phase disc was tested in the same manner as described in Example 9.

With respect to the (air side) surface deformation, the oxygen flux was increased about three times under the air / helium gradient, which means that the surface exchange kinetics on the air was improved by increasing the surface area for the oxygen glass through surface modification.

Table 4 Results for dual-phase disks

Disk area Disc thickness (mm) Feed flow rate (sccm) Purge flow rate (sccm) Ion permeation temperature (캜) O ₂ flux (sccm / cm 2) The corrected O ₂ flux (sccm / cm 2) Uncoated dual-phase disc (Example 9) 3.9 0.9 500 500 900 0.07 (0.06) * A dual-phase disk with a 1 mm porous coated LSFCCM on the air side (Example 10) 3.9 0.6 500 500 900 0.26 (0.16) *

* (Flux corrected for 1 mm thick film)

The features of the present invention are shown in one or more drawings only for convenience of explanation, and each feature may be combined with other features in accordance with the present invention. Those skilled in the art will recognize alternative embodiments, which, of course, should be understood to be within the scope of the claims. For example, suitable first phase materials may conduct protons ions with or in place of oxygen ions in connection with a material containing hydrogen.

Has improved mechanical properties, can minimize microcracks during fabrication, does not require special atmospheres during processing or operation, is adapted to temperature and atmospheric changes, and has a limit imposed by surface kinetics and / or chemical kinetics To provide a high oxygen flux, and also to provide a solid electrolyte ion permeable membrane having a modified surface that provides an improved catalytic effect to the ion permeable membrane.

Claims (10)

A solid electrolyte ion-permeable membrane having a first surface and a second surface, A matrix material that conducts one or more ion types, and And at least one component that is physically distinguishable from the matrix material, The component improves at least one of mechanical properties, catalytic properties, and sintering properties of the matrix material, and the component is introduced into the matrix material to form a polyphase composite material, A solid electrolyte ion permeable membrane present in such a way as to prevent continuous electronic conduction through this component. The solid electrolyte ion permeable membrane according to claim 1, wherein the matrix material is a mixed conductor exhibiting both electron and oxygen ion conductivity. The solid electrolyte ion permeable membrane of claim 1, wherein the component is a metal present in such a way that the component is less than the percolation limit of electrons across the membrane. The method of claim 1, wherein the component is selected from the group consisting of silver, palladium, platinum, gold, rhodium, ruthenium, tungsten, tantalum, titanium, nickel, silicon, lanthanide, yttrium, copper, cobalt, chromium, vanadium, zirconium, manganese, molybdenum , Niobium, aluminum, iron, or a mixture thereof. The solid electrolyte ion-permeable membrane according to claim 1, wherein the constituent component is a non-metallic material. The solid electrolyte ion-permeable membrane according to claim 1, wherein the constituent components are in the form of non-metallic fibers. The solid electrolyte ion-permeable membrane according to claim 1, wherein the component further improves at least one of sintering action and catalytic property of the matrix material. The solid electrolyte ion-permeable membrane of claim 1, further comprising a porous coating disposed on at least one surface of the first and second surfaces of the membrane to enhance the surface reaction rate associated with the gas species. . The solid electrolyte ion permeable membrane of claim 8, wherein the porous coating comprises a mixed conducting material exhibiting both electronic conductivity and oxygen ion conductivity. The solid electrolyte ion permeable membrane of claim 8, wherein at least one of the dense membrane and the porous membrane is disposed on the porous support to improve the structural stability of the membrane.

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